This invention relates to mounting rollers, such as electrophotographic developer rollers, to be protected from being damaged or deformed by lateral forces. Such forces may come from drive forces employing helical gears or from external impact such a being dropped.
Rollers such as electrophotographic developer rollers are relatively pliable cylindrical masses mounted on a steel shaft. (The cylindrical mass will be termed here the xe2x80x9croller body.xe2x80x9d) The steel shaft is inherently resistant to deformation. Deformation of the roller body by lateral forces can cause the support frame to impact gears mounted on the shaft, which can destroy the gear operation. Additionally, deformation of the roller body by lateral forces results in uneven development and escape of toner out of the electrostatic device, both events being unacceptable.
Prior rollers are known which provide a circular ledge in the support shaft on each side of the support shaft. The roller body is located between the ledges. The ledges, as well as edges of the roller body contact the frame. This can be acceptable where the gear on the shaft is press fit and can be moved slightly when dropped, and where toner escape is prevented by the frame being sufficiently stiff.
A prior assembly for preventing lateral forces on the roller body is understood to provide a notch for a C clip spaced a short distance from the ledge at each ledge. The notches are positioned immediately past the frame holding the roller, so that the C clip in each notch prevents significant lateral movement by abutting the frame. (The frame at this location normally includes a bearing in which the shaft is inserted.) The shaft is held in one lateral direction by one of the C clips abutting the frame and the shaft is held in the other lateral direction by the other C clip abutting the frame.
Such an assembly, however, does not protect a gear mounted on the shaft when the frame deflects so much that a C clip is displaced. Similarly, such an assembly does not protect the roller body when the frame deflects so much that the roller body comes in contact with the frame or another element on the side of the assembly. Moreover, it is desirable to eliminate the C clips, as they are separate elements having some cost and some potential of failure and are difficult to repair.
In accordance with an implementation of this invention a ledge is provided on each side of the roller shaft. On one end of the shaft the ledge abuts the frame element to protect the roller body from lateral movement in one direction in the manner of the ledge in of the foregoing prior assembly. A unique, first bearing and frame combination is provided to receive the shaft on the other end of the shaft. The first bearing has a small width and a larger width, the larger width having an extended part. The frame has an opening to allow the bearing to enter when the small width faces the opening and has a cavity to receive a part of the larger width when the bearing is rotated. The cavity has an outer wall that is part of the frame.
The first bearing has a central hole in which the shaft is inserted. The opposite end of the shaft is inserted into a conventional, second bearing in the frame on the side opposite to the first bearing. The second bearing may be conventional when it is in a stiff element such as a gear plate. With the shaft inserted, the first bearing is rotated so that its small width fits into the frame opening and is then inserted into that frame opening. Then the first bearing is rotated so that the extended part is in the cavity of the frame.
In this assembly both sides of the shaft abut the bearings, which are part of the frame. Therefore, the roller body is prevented from coming in contact with the frame.
In an embodiment, the shaft carries a helical gear, which is positively attached to the shaft, specifically by a snap fit on the gear that mates with a notch fitted into a ledge in the shaft. This positions the gear against movement by lateral forces caused by the helical gear design, which permits the gear assembly to be compact and carry large forces. The gear is prevented from being stripped out of the notch when the cartridge is subjected to large lateral forces by the shaft being firmly positioned with respect to the frame.
The first bearing preferably is electrically conductive and has an extended part on its outside past the frame for contact with an electrical contact pad in a cartridge in which the roller is mounted.